Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ALA~ CIRCUIT FOR CAR _LTERNATOR
The invention relates to an alarm circult for
an alternator for charging a car battery.
The object of the invention is to pro~ide an
alarm circuit for lndicating a defect such as non-
rotation or de-energization in a car battery charging
alternator, this al~ernator comprising at least two
terminals, one posi~ive~ one negative~ connected to the
armature by one or more rectifi.er diodes.
According to the invention, the alarm circuit
comprises a voltage divider formed by two resistors in
series connected between a positive terminal and a negative
terminal of the alternator, the centre poin~ of this
divider being connected to the control terminal of an
electronic commutation circuit provided in series with a
warning device between the terminals of the batter~, and
rectifier means being provided in the supply circult of
the battery for avoiding said latter to discharge through
the voltage divider.
The electronic commutation cirruit ~s for example
a transistor circuit of which the ou~put path is closed
when the v~ltage applied to the control electrode reaches
a pred~termined valuer either when increas'ng or d~creasing.
In particular, a Darlington circuit may be used having a
base electrode connected to the centre point of the v~ltage
divider and a collector-emitter output pat~ ser.ially
connected with the warning device.
~lore particlllarly, there is provided:
An ala_m circuit for indicating a defec~ in a diode- ;:
recti.ied alternator for charging a car battery havillg positive
and negative terminals connected for charging, r~spectively;
to first and second alternator output te~minals of s~id
alternator at which rectified positive and negative vol.ages
35 are provided, the volta~e betwee~ said first and second alter~-
nar.or outpuL terminals ~eing maint~inPd at a normal runnlng
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output voltage for charging the battery during normal alterna-
tor operation, said alarm circuit comprising:
an electrical commutation circuit ha~ing an oukpu~ path
and a control terminal for providing cu~rent 1OW through
said output path in response to when a control voltaye at ~he
control terminal exceeds a predeterm.ined threshold voltage
with respect to said second alternatox output terminal,
a warning device connected with and con~rolled by said
output path between said battery termina~s, and
a voltage diviaer for providing said control voltage,
said divider having a central point connected to said control
terminal and two end terminals connected, respectively, to
first and second auxiliary terminal~ of said alternator,
said first and second auxiliary texminals providing potentials
substantially equal to the potentials at said first and second
alternator output terminals, respectively, during the normal
running operation of said alternator,
wherein said first auxiliary alternatox term~l and said
first alternator output terminal are directly connected
together to be maintained at subst~ntially the same potential,
while diode means are coupled betwe~n said second auxilia~y
terminal anc~ sai~l secon~ a~ ~er~ato~: o~:~ut ~ermina7 t:o ~ ate
said second auxili~ry ~ermlnal a~d said ~oltage divider ~rom
~id second ~lt~na~or ~utput t~:~min~l ~nd unG o,f said posi-
tive and negative batte~y te~minals ~ whe~eln ~id diode meansprevents said battery from supplying curren~ 10w through said
voltage divider ~nd wherein said control voltage exceeds said
threshold voltage for both low and hi~h vol~age outputs lDetween
said first and second alternator output terminals thereby
3~ causing excitation of said warning device, and said control
voltage is less than said threshold voltage for the normal r~n-
The invention will ~e more readily understood
on read~n~ the fol'owing description w~th reference to
the ~ccompanying drawings, in wnich ~
Flg. 1 is a aiagram o~ the 21arm circul~ according
to ~he invention.
F~g~ 2 shows the connect~on of the a~mat~J~ o
the alternator t~ the di~eren~ ou~put t2rminals~
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Referring now to the drawings, the alternator
is three-phase and its armature is connected to -the
terminals B+ ancl B- of the battery supply clrcuit via
three rectifier diodes, one on each phase ; a thi~d
negative terminal D- is also connected ~o the ~rma-ture
by three diodes.
The alternator thexefore comprises two term~nals
B~ and B- for supplying the battery 1 which feeds the
variable load 2 ; it also comprises an excitation terminal
E which is supplied by a known regulator 3 connected to
the terminals B~ and B-.
Apart from these terminals, there are also
terminal D and an auxiliary terminal Baux. + which is
.connected directly to the terminal B-~.
The alarm circuit according to the invention
comprises a voltage divider formed by two resistors 4
and 5 in series connected between the terminals Baux. +
and D-, the centre point of this divider, i.e. the point
of junction of the resistors 4 and 5 is connected to the
base of a Darl~ngton circuit 6 of which the emitter is
connected to the negative terminal of the battery and
the.co~lector to the positlve terminal of the battery
via a warning lamp 7 and a switch 8.
The functlon~ng of the circuit when the swi.tch
is on makes it possible to indicate, by the lamp glowing,
the stopping of the alternator, the de-energi2ation thereof
and the disconnection of one of terminals E, B~ or B-.
If the alternator is stopped or not energized,
but rotating/ no voltage appears between the term~nals
B+ and D- and no current circulates in the divider since
. the dlodes of the tenminal B- isolate the b~ttery from
tarminal D-, the base of the Darlington circuit is at th~
positive potential of.th~ battery via the resistor 5 and
the Darlington circult 6 being saturated, the ba~tery
~eeds the lamp 7 collector-emittPr circuit of the
Darlin~ton circult 6 and the warning ~amp ~lows,
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If the positive terminal B-~ is discunnecte~,
the outpu~ voltage between B-~ aux. and D- is a function
of the speed of the al~rnator and always greater than
the regulation voltage, it follows that the base is at
a hiyh vol~age which saturates the Darlington c:Lrcu1t 6,
whereby the warning lamp g].ows.
In normal running with the alternator rota-ting,
the termlnal D- is at the same potent:ial as terminal B-,
the resistors 4 and 5 function as voltage divider and
their value is such that the potential applied to the
base of Darlington circuit 6 is lower than the limit of
conductions of the transistor and no current circulates
in the lamp 7 which is extinguished.
As above indicat~d~ the terminal D- is separated
lS by diodes ~m the terminal B- of the battery supply cir-
cuit. The battery does not discharge through the voltage
divider 4, 5 which is exclusively supplied with current
delivered by the alternator.
If the terminal D- does not exist, the resis-
tor 4 may be connected to the terminal B-, on condition
that an separating diode be inserted between the terminal
B~ and the negati~e terminal o the battery, avoid:ing
the battery feeding the voltage divider.
A sharp commutation of the load 2 results in
an overvoltage which saturates, for a certain period of
time, the battery 1, which provokes the blocking of the
xe~ulator 3 and consequently the de-energization of the
alternator which lights up the warning lamp.
This phenomenon is avoided by connecting means
to the ~ase of the Darlington circuit 6 fox eliminating
; the transient voltage variations, ~or example a capacitor
9 ~onnected between the base and the collector of the
Darlington circuit. The presence o the capacitor 9 will
n~t disturb ~he normal run~ing of the Darlington circuit
since the latter has a high gaLn and a high input impedance.
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